Conventionally, an ultrapure water producing apparatus for producing ultrapure water from raw water, such as city water, ground water and industrial water, is basically configured by a pre-treatment apparatus, a primary pure water producing apparatus and a secondary pure water producing apparatus. Among them, the pre-treatment apparatus is configured by coagulating, floating and filtering apparatuses. The primary pure water producing apparatus is configured, for example, by two reverse osmosis membrane separation apparatuses and a mixed bed ion-exchange apparatus or by an ion-exchange pure water apparatus and a reverse osmosis membrane separation apparatus. The secondary pure water producing apparatus is configured, for example, by a low-pressure ultraviolet ray oxidizing apparatus, a mixed bed ion-exchange apparatus and an ultra-filtration membrane separation apparatus.
In an ultrapure water producing apparatus as such, demands for improving the purity have been increasing and, along therewith, removal of TOC components has been demanded. Among the TOC components in ultrapure water, particularly urea is hard to be removed, and the more the TOC components are reduced, the more removal of urea affects a content of the TOC components. Therefore, removing TOC sufficiently in ultrapure water by removing urea from water to be supplied to an ultrapure water producing apparatus has been described in the patent articles 1 to 3.
The patent article 1 discloses incorporating a bio-treatment apparatus in a pre-treatment apparatus and decomposing urea by the bio-treatment apparatus. Also, in the patent article 2, a bio-treatment apparatus is incorporated in the pre-treatment apparatus and mixed water of water to be treated (industrial water) and collected water from semiconductor cleaning is brought to flow through it. And it is disclosed that organic substances contained in the collected water from semiconductor cleaning become a carbon source for bio-treatment reaction and improve decomposing speed of urea. Note that a large amount of ammonium, ions (NH4+) is included in the collected water from semiconductor cleaning in some cases, and they sometimes become a nitride source as same as urea and hinder decomposition of urea. Furthermore, the patent article 3 describes, in order to solve the problem in the patent article 2 above, that water to be treated (industrial water) and collected water from semiconductor cleaning are subjected to bio-treatment separately before being mixed and brought to flow through the primary pure water producing apparatus and secondary pure water producing apparatus.